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th400 will not shift in higher gears

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Old Jul 22, 2019 | 01:09 PM
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Default th400 will not shift in higher gears
my th400 in my 75 will not shift into higher gears unless i jump on it and let off....this is with the electrical wire to tranny disconnected.helphelp
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Old Jul 22, 2019 | 01:20 PM
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I had a similar problem this spring on my 74, mine was caused by a leaking hose on the vacuum modulator. It could also be that the modulator has failed. The modulator is on the passenger side of the tranny. There should be a steel line going from the intake manifold to the transmission with a short rubber hose on each end. Check the hose for cracks or dry rot and replace as needed. You can also check the modulator by pulling vacuum on it and seeing if it holds. If it does not the modulator should be replaced.
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Old Jul 22, 2019 | 03:57 PM
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took it out for a test run would not shift into high gear unless i put it in neutral and let off the gas, then shift to drive,,,,,the kick down works.
is it possible for the modulator valve to go bad........
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Old Jul 22, 2019 | 04:00 PM
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Originally Posted by the papster
took it out for a test run would not shift into high gear unless i put it in neutral and let off the gas, then shift to drive,,,,,the kick down works.
is it possible for the modulator valve to go bad........
Yes.....they are cheap.....replace it and check the vacuum line as stated.....

Jebby
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Old Jul 22, 2019 | 05:29 PM
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thanks bro i will do
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Old Jul 22, 2019 | 05:46 PM
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Originally Posted by the papster
thanks bro i will do
https://www.rockauto.com/en/catalog/...modulator,8500

Jebby
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Old Jul 22, 2019 | 07:00 PM
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vacuum line hooked up , went to test ,will no move in any gear...dododododododo.
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Old Jul 22, 2019 | 07:44 PM
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Originally Posted by the papster
vacuum line hooked up , went to test ,will no move in any gear...dododododododo.
Is it low on fluid?
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Old Jul 22, 2019 | 10:43 PM
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Does it shift manually?
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Old Jul 23, 2019 | 06:40 AM
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If vacuum mod is bad, it can suck fluid and burn it. So first it won't shift cuz mod is bad. Then it won't go cuz it sucked all the fluid out. Here's hoping....
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Old Jul 23, 2019 | 06:11 PM
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finally got it going, all new vacuum lines....has reverse low and no second and will not shift into high unless i let off the gas and put nit in neural then back in drive for third gear.


god bless your help guys , still could use a little
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Old Jul 23, 2019 | 06:56 PM
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Originally Posted by the papster
finally got it going, all new vacuum lines....has reverse low and no second and will not shift into high unless i let off the gas and put nit in neural then back in drive for third gear.


god bless your help guys , still could use a little
Check the transmission fluid level. The engine should be idling with car in park when you check it.
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Old Jul 23, 2019 | 07:34 PM
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Originally Posted by the papster
finally got it going, all new vacuum lines....has reverse low and no second and will not shift into high unless i let off the gas and put nit in neural then back in drive for third gear.


god bless your help guys , still could use a little
Repace the modulator and governor.....

Jebby
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